The present invention relates to a process for the preparation of esters of 1,5-dimethyl bicyclo [3.2.1] octan-8.ol and/or derivatives thereof. The present invention further relates to novel esters of 1,5-dimethyl bicyclo [3.2.1] octan-8-ol and derivatives thereof which may find application as plasticizers, fire retardent agents and which because of their thermal stability, can also be of interest as heat transfer liquids, e.g. in transformer oils, brake fluids, oil additives and in synthetic lubricants. They may also be used in the detergent and textile industry and may serve as precursors for certain aroma chemicals. The present invention relates in particular to the phosphate and sulphate esters of 1,5-dimethyl bicyclo [3.2.1] octan-8-ol.
Esters derived from 1,5-dimethyl bicyclo [3.2.1] octan-8-ol and carboxylic acids are described in Dutch patent application Nos. 7805142 and 7805143, respectively. They can be prepared by reacting 1,5-dimethyl-1,5-cyclooctadiene with the appropriate carboxylic acid, preferably in the presence of an acidic catalyst. It is also possible to prepare such esters by reacting the bicyclic alcohol (1,5-dimethyl bicyclo [3.2.1] octan-8-ol) with the appropriate carboxylic acid in the presence of an acidic ion exchange resin or by transesterification procedures.
It is not known, however, to prepare esters of 1,5-dimethyl bicyclo [3.2.1] octan-8-ol and inorganic acids. It is stated by J. K. Whitesell, R. S. Matthews and P. A. Solomon, Tetrahedron Letters No. 19, pp 1549-1552, 1976 that 1,5-dimethyl bicyclo [3.2.1] octan-8-ol can be obtained in 50% yield by reacting 1,5-dimethyl-1,5-cyclooctadiene with a solution of perchloric acid in a mixture of water and dioxane. No reference is made to the presence of the corresponding perchlorate. When the Applicants tried to prepare a sulphate ester of 1,5-dimethyl bicyclo [3.2.1] octan-8ol by reacting this compound with sulphuric acid, the only result was tarry substance. When phosphoric acid was brought into contact with 1,5-dimethyl bicyclo [3.2.1] octan-8-ol, no reaction was observed, not even at elevated temperature.
It has now surprisingly been found that esters of 1,5-dimethyl bicyclo [3.2.1] octan-8-ol and inorganic acids can be prepared in rather good yields and under very mild process conditions when 1,5-dimethyl-1,5-cyclooctadiene is reacted with an inorganic polybasic acid.